1. Statement of the Technical Field
The invention is directed to a loudspeaker system. In particular, the invention is directed to a system which protects a loudspeaker while maximizing the power that can be input to the loudspeaker.
2. Description of the Related Art
Sound reproduced by a portable handheld radio transceiver system is required to be loud enough to remain intelligible among environmental noises. For a small loudspeaker within a portable handheld radio transceiver system, this loudness may be achieved by driving the loudspeaker near its operational limits. However, driving a loudspeaker near its operational limits incurs a risk of overdriving the loudspeaker.
Overdriving a loudspeaker may disrupt the reproduction of an output sound in various manners. For example, overdriving a loudspeaker may cause elements of the loudspeaker to overheat, resulting in permanent damage or failure of the loudspeaker. Overdriving a loudspeaker may also risk distortion of the output sound, resulting in an abrupt and unpleasant attenuation of the output sound. The risk of overdriving a loudspeaker may be further complicated by environmental conditions, such as ambient temperature extremes in the environment of use. Such environmental conditions can cause a loudspeaker associated with a portable radio system to reach its operational limits at comparatively lower drive levels.
Simple protection schemes have been devised to address aspects of this risk. Yet, these schemes remain deficient in providing a proper degree of protection. For example, simple schemes involving feedback of an audio signal may not be able to prevent loudspeaker damage under unusual signal conditions, including when a protection scheme is unable to quickly respond. Moreover, simple protection schemes that rely on the level of an applied audio signal may not adequately account for one or more other time varying factors associated with a loudspeaker, such as a temperature, a period of time over which the audio signal is applied, and a waveform shape of the audio signal. These simple protection schemes may also reduce the loudness of the output sound unnecessarily. That is, simple protection schemes may overprotect a loudspeaker at the expense of an otherwise preferable and achievable output sound pressure level.